Thin film transistor liquid crystal display array substrate and manufacturing method thereof

ABSTRACT

A TFT LCD array substrate and a manufacturing method thereof. The manufacturing method includes the steps of: forming a thin film transistor on a substrate to form a gate line and a gate electrode connected with the gate line on the substrate; forming a gate insulating layer and a semiconductor layer on the gate electrode; forming an ohmic contact layer on the semiconductor layer; forming a transparent pixel electrode layer and a source/drain electrode metal layer in sequence on the resultant substrate, wherein the transparent pixel electrode layer is electrically insulated from the gate line and the gate electrode, and the transparent pixel electrode layer forms an ohmic contact with two sides of the semiconductor layer via the ohmic contact layer; and performing masking and etching with a gray tone mask with respect to the resultant substrate to form a transparent pixel electrode, a source/drain electrode and a data line simultaneously.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/096,380, filed Apr. 28, 2011 (pending/allowed), which is adivisional application of U.S. application Ser. No. 11/737,954, filedApr. 20, 2007, now U.S. Pat. No. 7,952,099 that issued May 31, 2011,which claims the priority of Chinese Patent Application Nos. CN200610074457.2 filed Apr. 21, 2006 and CN 200610080641.8 filed May 23,2006, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a thin film transistor liquid crystaldisplay (TFT LCD) array substrate and a manufacturing method thereof,and more particularly, to a TFT LCD array substrate manufactured withphotolithography processes using reduced number of masks and amanufacturing method thereof

BACKGROUND OF THE INVENTION

As one important type of flat plate display, a LCD, such as TFT LCD, hasbeen developing rapidly in the last decade and has attracted theattention. Due to intensive competition among the manufactures andadvancement in manufacturing technology of TFT LCD, LCDs with excellentdisplay performance and lower price have been increasingly put intomarket. Therefore, introduction of more advanced manufacturingtechnology to simplify the production process and reduce the productioncost has become an important guarantee for the manufacturer to survivein the intensive competition.

The manufacturing technology for TFT LCD array substrate has undergonethe map from the seven mask (7Mask) technology to the current five mask(5Mask) technology, and the 5Mask technology today has become themainstream for manufacturing TFT LCD array substrate.

Some manufacturers have attempted to exploit the four mask (4Mask)technology in fabrication. This 4Mask technology is based on theprevious 5Mask technology, in which the mask for forming active layer(Active Mask) and the mask for forming source/drain electrode (S/D Mask)are merged into a single one with the aid of gray tone mask, and thefunctions of the original two masks, i.e., Active Mask and S/D Mask, areachieved by the single mask through modification to the etchingprocesses.

Gray tone mask has a slit-shaped pattern thereon, and partiallytransparent patterned regions are formed on the mask due to theinterference and diffraction of light passing the patterned regions ofthe mask. During exposure, the light only partially passes through thepartially transparent portions. By controlling the exposure quantity,light passing through the partially transparent portions illuminatesportions of photoresist and has the portions partially exposed, and thelight passing through the remaining fully transparent portions of themask illuminates the other portions of the photoresist and has theseportions fully exposed. After developing, no photoresist exists in thefully exposed regions, and photoresist thickness in the partiallyexposed regions is less than that in the non-exposed regions, so thatthe exposed photoresist is shaped in three-dimension. The photoresistthickness can be controlled by controlling the transmittance ratio amongthe regions of the gray tone mask, i.e. the “duty ratio” of the slitregion to the empty region. The method of forming a three-dimensionalpattern with different thickness on the photoresist through a mask withpartially transparent pattern is collectively called gray tone masktechnology.

The conventional 5Mask technology uses five masks for photolithography,including the masks for forming gate electrode (Gate Mask), active layer(Active Mask), source/drain electrode (S/D Mask), via hole (Via HoleMask), and pixel electrode (Pixel Mask), respectively. The processesusing the respective masks further include one or more thin filmdeposition and etching process (e.g., dry etching or wet etchingprocess), thus resulting in five cycles of thin film deposition,photolithography, and etching processes, as shown in FIG. 2.

A typical pixel unit of a TFT LCD array substrate manufactured by theabove conventional 5Mask technology is shown in FIG. 1.

SUMMARY OF THE INVENTION

In line with the trend of the art, the present invention provides a TFTLCD array substrate and the manufacturing method thereof, which reducesthe photolithography using mask so as to reduce the process steps,improve the production capacity and decrease the cost, and also improvesthe utilization ratio of the equipment, reduces the process time andimproves the yield.

In order to achieve the above objects, according to one aspect of thepresent invention, there is provided a TFT LCD array substrate,comprising: a substrate and a pixel array on the substrate, each pixelcomprising: a gate line and a gate electrode connected with the gateline formed on the substrate; a gate insulating layer formed on the gateelectrode; a semiconductor layer formed on the gate insulating layer andan ohmic contact layer formed on the semiconductor layer; a transparentpixel electrode formed on the semiconductor layer and the ohmic contactlayer; a source/drain electrode formed on the transparent pixelelectrode and data line connected with the source/drain electrode; and apassivation layer formed on the source/drain electrode, the data lineand the transparent pixel electrode, wherein, the transparent pixelelectrode establishes an ohmic contact with the semiconductor layer viathe ohmic contact layer over two sides of the semiconductor layer.

According to another aspect of the present invention, there is provideda method of manufacturing the above TFT LCD array substrate, comprising:step 1 of depositing a gate metal layer on a substrate and thenperforming masking and etching to obtain a gate line and a gateelectrode connected with the gate line; step 2 of depositing a gateinsulating layer, an semiconductor layer, and an ohmic contact layer onthe resultant substrate after step 1 and then performing masking andetching to form the thin film transistor; step 3 of depositing atransparent pixel electrode layer and a source/drain electrode layer onthe resultant substrate after step 2 and then performing masking with agray tone mask to form a transparent pixel electrode, a source/drainelectrode, and a channel for the TFT; and, step 4 of depositing apassivation layer on the resultant substrate after step 3, and thenperforming masking and etching to form via holes and provide protectionfor the channels, with pad being exposed therein.

With the above method, a TFT LCD array substrate can be obtained with a4Mask method, which can be realized with fewer steps, lower productioncost, and higher yield compared with the conventional 5Mask process.Furthermore, by merging the mask for the source/drain electrode and maskfor transparent pixel electrode into a single one, the source/drainmetal layer and the transparent layer can be deposited sequentially inthe same sputter, and the yield and utilization ratio of the sputter canbe improved.

According to yet another aspect of the present invention, there isprovided another TFT LCD array substrate, comprising: a substrate and apixel array on the substrate, each pixel comprising: a gate line and agate electrode connected with the gate line, formed on the substrate; agate insulating layer formed on the gate electrode and a semiconductorlayer formed on the gate insulating layer; and an isolating dielectriclayer covering the substrate, the gate line, the gate electrode, thegate insulating layer and the semiconductor layer, wherein via holes, inwhich an ohmic contact layer is deposited, are formed on both sides ofthe isolating dielectric layer over the semiconductor layer, atransparent pixel electrode formed on the isolating dielectric layer andestablishing an ohmic contact with the semiconductor layer via the ohmiccontact layer in the via holes, and a source electrode, a drainelectrode and a data line formed on the transparent pixel electrode.

According to yet another aspect of the present invention, there isprovided a method of manufacturing the above TFT LCD array substrate,comprising: step 1 of depositing a gate metal layer, a gate insulatingdielectric layer and a semiconductor layer on a substrate, and thenperforming masking and etching by a gray tone mask to form a gate line,a gate electrode connected with the gate line, a gate insulating layer,and a semiconductor layer for a thin film transistor; step 2 ofdepositing an isolating dielectric layer on the resultant substrateafter step 1, and then performing masking and etching process withrespect to the isolating dielectric layer to form via holes in theisolating dielectric layer on both sides of the semiconductor layer;step 3 of forming an ohmic contact layer in the via holes obtained instep 2; and step 4 of depositing a pixel electrode layer and asource/drain electrode metal layer on the resultant substrate after step3, then performing masking and etching with a gray tone mask to form atransparent pixel electrode, a source electrode, a drain electrode and adata line, wherein the drain electrode is integrated with the data line.

With the above method, the masks used for fabrication of a TFT LCD arraysubstrate can be further reduced, and only three masks are possibly usedto obtain the TFT LCD array substrate. This 3Mask method go forward withless steps, lower production cost and higher yield compared with theconventional manufacturing process. Furthermore, by merging the mask forthe source/drain electrode and mask for transparent pixel electrode, thesource/drain metal layer and the transparent pixel electrode layer canbe deposited sequentially in the same sputter equipment, and the yieldand utilization ratio of the sputter can be improved.

Further, according to still another aspect of the present invention,there is provided a TFT LCD array substrate, comprising: a substrate anda pixel array on the substrate, each pixel comprising: a thin filmtransistor formed on the substrate, including a gate line and a gateelectrode connected with the gate line formed on the substrate, a gateinsulating layer formed on the gate electrode, a semiconductor layer,and an ohmic contact layer formed on at least two ends of thesemiconductor layer; a transparent pixel electrode formed on thetransistor, electrically insulated from the gate electrode and the gateline, and electrically contacted with the two ends of the semiconductorlayer respectively via the ohmic contact layer; and a source/drainelectrode and a data line formed on the transparent pixel electrode andelectrically connected with the semiconductor layer with the transparentpixel electrode.

According to still another aspect of the present invention, there isprovided a method of manufacturing the above TFT LCD array substrate,comprising: forming a thin film transistor on a substrate so thatforming a gate line and a gate electrode connected with the gate line onthe substrate, a gate insulating layer, a semiconductor layer on thegate electrode, and an ohmic contact layer on the semiconductor layer;forming a transparent pixel electrode layer and a source/drain electrodemetal layer in sequence on the resultant substrate, wherein thetransparent pixel electrode layer is electrically insulated from thegate line and the gate electrode, and the transparent pixel electrodelayer forms an ohmic contact with two sides of the semiconductor layervia the ohmic contact layer; and performing masking and etching with agray tone mask with respect to the resultant substrate to form atransparent pixel electrode and a source/drain electrode simultaneously,wherein the partially transparent portion of the gray tone maskcorresponds to the transparent pixel electrode, the opaque portion ofthe gray tone mask to the source/drain electrode and the data line, andthe completely transparent portion of the gray tone mask to theremaining portion of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail with reference to theaccompanying drawings which illustrate the preferred embodiments of thepresent invention, in which:

FIG. 1 is a plan view of a typical pixel unit of a TFT LCD arraysubstrate;

FIG. 2 is the conventional 5Mask method's flowchart;

FIG. 3 is the flowchart in accordance with the first embodiment of thepresent invention;

FIG. 4 is a plan view showing a typical pixel unit of a TFT LCD arraysubstrate obtained in accordance with the first embodiment of thepresent invention;

FIG. 5 is a cross-sectional view along the line A-A in FIG. 4;

FIG. 6A is a plan view illustrating a stage after the Gate Mask of step1 (S11) in accordance with the first embodiment;

FIG. 6B is a cross-sectional view along the line A-A in FIG. 6A;

FIG. 7A is a plan view illustrating a stage after the Active Mask ofstep 2 (S12) in accordance with the first embodiment;

FIG. 7B is a cross-sectional view along the line A-A in FIG. 7A;

FIG. 8A is a plan view illustrating a stage after G/T S/D Mask;

FIG. 8B is a cross-sectional view along the line A-A in FIG. 8A;

FIG. 9A is a plan view illustrating a stage after the Via Hole Mask;

FIG. 9B is a cross-sectional view along the line A-A in FIG. 9A;

FIG. 10 is the flowchart in accordance with the second embodiment of thepresent invention;

FIG. 11 is a plan view showing a typical pixel unit of a TFT LCD arraysubstrate obtained in accordance with the second embodiment of thepresent invention;

FIG. 12A is a cross-sectional view along the line A-A in FIG. 11;

FIG. 12B is a cross-sectional view along the line B-B in FIG. 11;

FIG. 13A is a plan view illustrating a stage after the first maskingwith a gray tone mask and etching in accordance the second embodiment ofthe present invention;

FIG. 13B is a cross-sectional view along the line C-C in FIG. 13A;

FIG. 14A is a plan view illustrating a stage after the Via Hole maskingand etching in accordance with the second embodiment of the presentinvention;

FIG. 14B is a cross-sectional view along the line D-D in FIG. 14A;

FIG. 15A is a cross-sectional view showing an ohmic contact layer formedby the first approach in accordance with the second embodiment of thepresent invention;

FIG. 15B is a cross-sectional view showing an ohmic contact layer formedby the second approach in accordance with the second embodiment of thepresent invention; and

FIG. 15C is a cross-sectional view showing an ohmic contact layer formedby the third approach in accordance with the second embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is provides for convenience in identifying the elements ofthe drawings:

1: substrate

2: gate line and gate electrode

3: gate insulating layer

4: semiconductor layer

15: ohmic contact layer

5: pixel electrode

6: source/drain electrode (data line)

7: passivation layer

9: high temperature photoresist

10: Mo (W, Cr, or alloys thereof) layer

17: isolating dielectric layer

Hereinafter, the present invention will be described more fully byreference to the accompanying drawings, in which the preferredembodiments of the present invention are illustrated. However, thepresent invention can be carried out in many ways, and should not beconstrued to be limited to the preferred embodiments illustrated herein.On the contrary, these embodiments are provided to make the disclosuremore sufficient and complete, and fully convey the scope of the presentinvention to those skilled in the art.

The First Embodiment

FIG. 3 illustrates the detailed flowchart for the method ofmanufacturing a TFT LCD array substrate in accordance with the firstembodiment of the present invention, which includes the following steps.

In Step 1 (S11), on a substrate 1 such as a glass substrate, a gatemetal layer such as Mo/AlNd/Mo (400Å/4000 Å/600 Å) laminate layer isdeposited for example by magnetron sputtering. Then, a masking (GateMask) is performed on the gate metal layer, and a wet etching isperformed to form a gate line (not shown) and gate electrode 2, as shownin FIGS. 6A and 6B.

Alternatively, the gate metal layer deposited in this step can be asingle layer of AlNd, Al, Cu, Mo, MoW or Cr, and can also be a compositefilm composed of any combination of AlNd, Al, Cu, Mo, MoW, and Cr, forexample, metallic composite film of Mo/AlNd/Mo or AlNd/Mo.

In Step 2 (S12), on the resultant substrate after etching the gate metallayer, a gate insulating layer 3, a semiconductor layer (active layer)4, and an ohmic contact layer (i.e., SiNx/a-Si/μc-Si (5000 Å/2000 Å/500Å) layers) are deposited in sequence by plasma enhanced chemical vapordeposition (PECVD) process. Here, in order to ensure the ohmic contactbetween the semiconductor layer and a transparent pixel electrode to beformed later, microcrystal silicon (μc-Si) material is used for theohmic contact layer instead of n⁺a-Si. Then a masking (Active Mask) isperformed on the active layer, and an etching is performed to form theactive layer of the TFT, as shown in FIGS. 7A and 7B (the ohmic contactlayer of μc-Si is not shown). The microcrystal silicon material is forexample phosphor (P)-doped microcrystal silicon, i.e., n⁺μc-Si, so as toachieve better electrical conductivity.

Alternatively, the gate insulating layer in this step can be a singlelayer of SiNx, SiOx, or SiOxNy, or a composite film composed of anycombination of SiNx, SiOx, and SiOxNy.

In Step 3 (S13), a transparent pixel electrode layer (e.g., ITO of 500Å) and source/drain electrode layer (e.g., Mo of 3000 Å) are depositedsequentially by magnetron sputtering. Then, a mask is applied under thegray tone mask technology on the resultant substrate, wherein theportion of the mask corresponding to the transparent pixel electrode tobe formed is partially transparent, the portion of the maskcorresponding to the source/drain electrode and the data line to beformed is opaque, and the remaining portion of the mask is transparent,so that a three-dimensional mask is formed on the substrate by exposingand developing photoresist. With the three-dimensional mask formed afterexposing and developing, an etching (G/T S/D etching) for thetransparent pixel electrode and the source/drain electrode and anetching for ohmic contact layer μc-Si are performed in order to form thetransparent pixel electrode, source/drain electrode, and data lines,while forming the channel for the TFT, as shown in FIGS. 8A and 8B(μc-Si in the channel is not shown). In this step, the source/drainelectrode layer and the transparent pixel electrode layer can bedeposited sequentially in the same sputter, so that not only the yieldbut also the utilization ratio of the sputter can be improved.

Alternatively, the source/drain electrode layer can be a single layer ofMo, MoW, or Cr, or a composite film composed of any combination of Mo,MoW, and Cr. The source/drain electrode layer and the transparent pixelelectrode layer can be deposited sequentially in different sputter.

In Step 4 (S14), a passivation layer 7 is deposited by PECVD to athickness of about 2600 Å on the substrate. Then masking and etching forthe passivation layer 7 are performed sequentially, so as to form viaholes and provide protection for the channel, with the pad beingexposed, as shown in FIGS. 9A and 9B.

The first embodiment of the present invention provides a novel 4Maskprocess for manufacturing a TFT LCD array substrate, which is differentfrom the existing 5Mask and 4Mask processes. With the inventive 4Maskprocess of the embodiment, a complete TFT array substrate can beobtained with less steps, lower production cost and higher yield.Meanwhile, by depositing the source/drain metal layer and thetransparent pixel electrode layer sequentially in the same sputter, theyield and utilization ratio of the sputter can be improved.

Furthermore, the first embodiment provides a TFT LCD array substrate, asshown in FIGS. 4 and 5. The TFT LCD array substrate includes a substrate1, a gate line and a gate electrode 2 formed on the substrate 1, an gateinsulating layer 3 formed on the gate electrode 2, a semiconductor layer4 and an ohmic contact layer on the semiconductor layer 4, a transparentpixel electrode 5, a source/drain electrode 6 and a data line, and apassivation layer 7. Herein, the ohmic contact layer is comprised ofP-doped μc-Si material, and the transparent pixel electrode 5 isprovided above the ohmic contact layer in the source/drain region on thetwo sides of the semiconductor layer 4. An ohmic contact is achieved viathe μc-Si material, and the source/drain electrode is formed over thetransparent pixel electrode 5.

This embodiment only presents a specific solution for realizing thepresent invention, but the device configuration and the processconditions in this embodiment can be varied if desired. For example, anegative photoresist can be used, the structure and thickness ofindividual layers can be changed, other methods of physical vapordeposition (PVD) such as evaporation, electron beam evaporation, plasmaspray and the like, and chemical deposition methods such as atmosphericpressure CVD and the like can be employed, and dry etching such asplasma etching, reactive ion etching (RIE) and the like can be used. Thespecific process conditions of these methods can be varied depending onthe specific requirements during manufacturing the LCD, but thesevariations do not depart from the spirit and scope of sequentiallydepositing the transparent pixel electrode layer and the source/drainelectrode layer and forming the transparent pixel electrode andsource/drain electrode with the same gray tone mask.

The Second Embodiment

FIG. 10 illustrates the detailed flowchart for the manufacturing methodof a TFT LCD array substrate in accordance with the second embodiment ofthe present invention, which includes the following steps.

In Step 1 (S21), a gate metal layer is deposited on a clean glasssubstrate by sputtering. Then, a gate insulating layer and asemiconductor layer are deposited in sequence by plasma enhancedchemical vapor deposition (PECVD) method. The gate line and gateelectrode as well as the gate insulating layer and semiconductor layerof the TFT are obtained, with a gray tone mask, in which the partiallytransparent portion of the mask corresponds to the gate line and gateelectrode to be formed, the opaque portion of the mask corresponds tothe semiconductor layer of the TFT to be formed, and the transparentportion of the mask corresponds to the remaining portion of thesubstrate, by exposing, developing, and etching, as shown in FIGS. 13Aand 13B.

The gate metal layer deposited in this step can be a single layer ofAlNd, Al, Cu, Mo, MoW or Cr, and can also be a composite film composedof any combination of AlNd, Al, Cu, Mo, MoW, and Cr. The gate insulatinglayer deposited in the step can be a single layer of SiNx, SiOx, orSiOxNy, or a composite film composed of any combination of SiNx, SiOx,and SiOxNy.

In Step 2 (S22), on the resultant substrate of the previous step, anisolating dielectric layer is deposited for example by plasma enhancedchemical vapor deposition (PECVD). Then masking and etching processesare carried out to obtain via holes on both sides of the semiconductorlayer of the TFT respectively, which are prepared for ohmic contactbetween the pixel electrode layer and the semiconductor layer, as shownin FIGS. 14A and 14B.

The isolating dielectric layer deposited in this step can be a singlelayer of SiNx, SiOx, or SiOxNy, or a composite film composed of anycombination of SiNx, SiOx, and SiOxNy.

Then, in Step 3 (S23), an ohmic contact layer is formed in the via holesmade in the previous step.

The ohmic contact between the pixel electrode (as well as thesource/drain electrode) and the semiconductor layer can be realized inmany approaches, as long as an ohmic contact can be formed in the viaholes. FIGS. 15A-15C illustrate three different approaches respectivelyas follows.

In the first approach, as shown in FIG. 15A, mixed gas of PH₃ and H₂with certain ratio is introduced into the PECVD chamber, and a surfacereaction occurs on the exposure part of semiconductor a-Si layer in thevia holes under properly controlled reaction conditions such as suitablegas ratio, reaction temperature, plasma power, etc. The amorphoussilicon is induced to crystallize by H₂ plasma and form a μc-Si layer.Moreover, due to the presence of PH₃ plasma, P diffuses at the surfaceand eventually forms a P-doped μc-Si (n30 μc-Si) layer as an ohmiccontact layer, which is prepared for the ohmic contact between the pixelelectrode layer to be deposited hereafter and the semiconductor layerwith the P-doped μc-Si layer.

In the second approach, as shown in FIG. 15B, a high temperaturephotoresist is used for the mask in step 2, and the photoresist lift-offprocess is not performed at the end of the process. A P-doped μc-Silayer is directly deposited by PECVD on the resultant substrate, and thephotoresist along with the P-doped μc-Si layer thereon is stripped offby photoresist lift-off process, thereby obtaining the same structure asthe first approach, which is prepared for the ohmic contact between thepixel electrode layer to be deposited hereafter and the semiconductorlayer with the P-doped μc-Si layer.

In the third approach, as shown in FIG. 15C, a high temperaturephotoresist is used for the mask in step 2, and the photoresist lift-offprocess is not performed at the end of the process. On the resultantsubstrate, a n⁺ a-Si layer is deposited by PECVD and then a very thin Mo(or Cr, W, or alloys thereof) metal layer is deposited. The photoresistalong with the n⁺ a-Si layer and a Mo (or Cr, W, or alloys thereof)metal layer thereon is stripped off by photoresist lift-off process,thereby obtaining the same structure as the above approaches, so as tobe ready to establish the ohmic contact between the pixel electrodelayer to be deposited hereafter and the semiconductor layer with the n⁺a-Si layer and Mo (or Cr, W, or alloys thereof) metal layer.

In Step 4 (S24), after the above steps, the pixel electrode layer andthe source/drain electrode metal layer are sequentially deposited bysputtering. The pixel electrode, the source/drain electrode and the dataline thus can be obtained with a gray tone mask, in which the partiallytransparent portion of the mask corresponds to the pixel electrode to beformed, the opaque portion of the mask corresponds to the source/drainelectrode and the data line to be formed, and the transparent portion ofthe mask corresponds to the remaining portion of the substrate, byexposing, developing, and etching.

The source/drain electrode metal layer deposited in this step can be asingle layer of Mo, MoW or Cr, and can also be a composite film composedof any combination of Mo, MoW, and Cr.

After completion of the above steps, there is provided a TFT LCD arraysubstrate as shown in FIGS. 11, 12A and 12B, including the gate line andgate electrode 2 formed on the substrate 1, the gate insulating layer 3,and the semiconductor layer 4. Here, an isolating dielectric layer 17covers the substrate 1, the gate line and gate electrode 2, the gateinsulating layer 3, and the semiconductor layer 4. Via holes, in whichthe ohmic contact layer 15 is deposited, are formed in the isolatingdielectric layer 17 on both sides of the semiconductor layer 4. Thepixel electrode 5 establishes an ohmic contact with the semiconductorlayer 4 via the ohmic contact layer 15 in the via holes. Thesource/drain electrode is positioned above the pixel electrode 5, andthe data line 6 is integrated with the drain electrode.

Besides the P-doped μc-Si material, the ohmic contact layer 15 can be acomposite layer composed of n⁺a-Si layer and Mo, Cr, W, or alloy metallayers thereof The gate line and the gate electrode can be a singlelayer of AlNd, Al, Cu, Mo, MoW or Cr, and can also be a composite filmcomposed of any combination of AlNd, Al, Cu, Mo, MoW, and Cr. The gateinsulating layer 3 or the isolating dielectric layer 17 can be a singlelayer of SiNx, SiOx or SiOxNy, or a composite film composed of anycombination of SiNx, SiOx, and SiOxNy. The source/drain electrode or thedata line 6 can be a single layer of Mo, MoW or Cr, and can also be acomposite film composed of any combination of Mo, MoW, and Cr.

Thereinafter, the preferred example of the manufacturing method of thesecond embodiment according to the present invention will be describedby reference to the accompanying drawings.

The manufacturing method of a TFT LCD array substrate in accordance withthe second embodiment of the present invention includes following thesteps.

In Step 1 (S21), as shown in FIGS. 13A and 13B, a metal layer such asMo/AlNd/Mo (400 Å/4000 Å/600Å) laminate layer is deposited on thesubstrate 1 (made of glass or quartz) by sputtering. Then SiNx/a-Silayers (5000 Å/1000Å) are deposited in sequence by PECVD. Then, masking,exposing and developing are performed with a gray tone mask, andreactive ion etching (RIE) is used to form the gate lines and gateelectrode 2, the gate insulating layer 3, and the semiconductor layer 4of the TFT.

In Step 2 (S22), as shown in FIGS. 14A and 14B, an isolating dielectriclayer 7, which is a SiNx layer (2000 Å), is deposited on the resultantsubstrate after step 1 by PECVD. After masking for via holes, a dryetching is used to etch out via holes on both sides of the isolatingdielectric layer over the semiconductor layer, through which ITO isconnected with a-Si via an ohmic contact layer.

In Step 3 (S23), an ohmic contact layer 15 is formed on the resultantsubstrate after step 2 with the following approaches.

In the first approach, as shown in FIG. 15A, the mixed gas of PH₃(10000sccm) and H₂(5000 sccm) is introduced in the PECVD chamber and ansurface reaction occurs on the exposure part of a-Si layer in the viaholes formed in step 2 under proper temperature (300° C.), chamberpressure(2500 mtorr) and plasma power(3000 W), thereby forming a n⁺μc-Si layer (˜200 Å).

In the second approach, as shown in FIG. 15B, a high temperaturephotoresist 9 is used for the mask for via holes in step 2, and afteretching the high temperature photoresist 9 is not stripped off. A n⁺μc-Si layer (200 Å) is deposited by PECVD, and unwanted portions of then⁺ μc-Si layer along with the photoresist is stripped off by photoresistlift-off process, thereby the n⁺ μc-Si layer only remains in the viaholes.

In the third approach, as shown in FIG. 15C, a high temperaturephotoresist 9 is used for the mask for via holes in step 2, and afteretching the high temperature photoresist 9 is not stripped off. A layerof n⁺ a-Si (200 Å) is deposited by PECVD, a Mo (Cr, W, or alloysthereof) metal layer is deposited by sputtering, and unwanted portion ofthe n⁺ a-Si layer and the Mo (Cr, W, or alloys thereof) metal layeralong with the photoresist is stripped off by photoresist lift-offprocess, thereby the n⁺ a-Si layer and the Mo (Cr, W, or alloys thereof)metal layer only remain in the via holes.

In Step 4 (S24), on the substrate after step 3, an ITO (500 Å) layer andMo (Cr, W, or alloys thereof) (3000 Å) metal layer are sequentiallydeposited by sputtering. Then, masking, exposing, developing, andetching are performed with a gray tone mask, to form the pixel electrode5, the source/drain electrode and data line 6, in which the data line 6is integrated with the drain electrode, as shown in FIGS. 11, 12A and12B.

The second embodiment of the present invention provides a novel 3Maskmethod for manufacturing a TFT LCD array substrate, which is differentfrom the existing 5Mask and 4Mask methods. With the inventive 3Maskprocess, a complete TFT array substrate can be obtained with lessprocess steps, lower production cost and higher yield, and the yield andutilization ratio of the sputter equipment can also be improved.

The second embodiment also only presents a specific solution forrealizing the present invention, but the device configuration and theprocess conditions in this embodiment can be varied, but thesevariations should not depart from the spirit and scope of sequentiallydepositing the transparent pixel electrode layer and the source/drainelectrode layer and forming the transparent pixel electrode andsource/drain electrode with the same gray tone mask. Furthermore,similar to the first embodiment, other methods well known in the art canbe utilized to implement the deposition, etching, and the like of theindividual layer. Furthermore, in the method of forming the μc-Sicontact layer described above, the doped μc-Si layer can also be dopedwith impurities like arsenic (As) to obtain electrical conductivity.

It should be understood by those skilled in the art that the presentinvention can be varied and modified without departing from the spiritand scope thereof. Accordingly, the present invention is intended tocover all the changes and modifications as long as they fall within theappended claims and their equivalents.

We claim:
 1. A method of manufacturing a TFT LCD array substrate,comprising the steps of: 1) forming a thin film transistor on asubstrate, comprising forming a gate line and a gate electrode connectedwith the gate line on the substrate, a gate insulating layer, asemiconductor layer on the gate electrode, and an ohmic contact layer onthe semiconductor layer; 2) forming a transparent pixel electrode layerand a source/drain electrode metal layer in sequence on the resultantsubstrate, wherein the transparent pixel electrode layer is electricallyinsulated from the gate line and the gate electrode, and the transparentpixel electrode layer establishes an ohmic contact with two sides of thesemiconductor layer via the ohmic contact layer; and 3) performingmasking and etching with a gray tone mask with respect to the resultantsubstrate to form a transparent pixel electrode, a source/drainelectrode, and a data line simultaneously, wherein a partiallytransparent portion of the gray tone mask corresponds to the transparentpixel electrode to be formed, a opaque portion of the gray tone mask tothe source/drain electrode and the data line to be formed, and atransparent portion of the gray tone mask to remaining portion of thesubstrate.
 2. The method according to claim 1, wherein forming a thinfilm transistor on the substrate comprises the steps of: depositing agate metal layer on the substrate, then performing masking and etchingwith respect to the gate metal layer to obtain the gate line and thegate electrode connected with the gate line; and depositing an gateinsulating layer, a semiconductor layer, and an ohmic contact layer onthe resultant substrate, then performing masking and etching to form thethin film transistor, wherein the transparent pixel electrode layer isinsulated from the gate line and gate electrode via the gate insulatinglayer.
 3. The method according to claim 2, further comprises depositinga passivation layer on the resultant substrate after forming thetransparent pixel electrode, source/drain electrode, and date line, andthen performing masking and etching to form via holes and provideprotection for channel of the TFT, with pad being exposed therein. 4.The method according to claim 1, wherein forming a thin film transistoron the substrate comprises the steps of: depositing in sequence a gatemetal layer, a gate insulating dielectric layer and a semiconductorlayer on a substrate, then performing masking and etching with a graytone mask to form the gate line, the gate electrode connected with thegate line, the gate insulating layer, and the semiconductor layer;depositing an isolating dielectric layer on the resultant substrate,then performing masking and etching to form via holes in the isolatingdielectric layer on both sides of the semiconductor layer; and formingan ohmic contact layer in the resultant via holes; wherein thetransparent pixel electrode layer is insulated from the gate line andgate electrode via the isolating dielectric layer.
 5. The methodaccording to claim 1, wherein the ohmic contact layer is formed bydepositing μc-Si material.